Growth of Single-walled Carbon Nanotubes at Low Temperature and Low Pressure Cvd Conditions

Controlling the detailed structures of single-walled carbon nanotubes (SWNTs) is imperative for realizing many SWNT applications, and understanding the SWNT growth mechanism is important to improve the growth techniques. In the present study, we performed SWNT growth by a catalytic chemical vapor deposition (CVD) method in wide temperature and pressure ranges, using a high-vacuum CVD chamber. We focused on low CVD gas pressure and low temperature conditions and investigated the SWNT growth mechanism. SWNTs were synthesized by using ethanol gas as the carbon source. As the catalyst, Co and Mo metal nano-particles deposited onto silicon substrates were used. SWNTs were grown via the reaction between ethanol gas and the catalytic metal nano-particles at high temperature. The ethanol gas pressure ranged from 10 -3 Pa to 10 2 Pa, and the CVD temperature ranged from 400 to 900 °C. The yield of SWNTs was assumed to be proportional to the G-band intensity, which was measured by Raman scattering spectroscopy. SWNT samples were observed by scanning electron microscopy and transmission electron microscopy. An optimum CVD temperature existed for each ethanol gas pressure, and decreased with decreasing ethanol gas pressure. Moreover, SWNTs were grown even at 500 °C, when the ethanol gas pressure was low (less than 10 -2 Pa). In this study, the minimum temperature and pressure at which SWNTs could be grown were 450 °C and 10 -3 Pa. At low temperature and low CVD gas pressure, the activity of the catalyst and the growth rate of SWNTs were low, while the catalyst lifetime was long. INTRODUCTION Single-walled carbon nanotube (SWNT) is a rolled up graphene sheet, which was discovered by S. Iijima et al., in 1993 [1]. The diameter of an SWNT is a few nm, whereas the length can be several millimeters. Owing to this onedimensional structure, SWNTs have various exceptional properties, which motivate much research in many related fields. Some of the SWNT properties strongly depend on the chiral structure, which is described by the chiral vector Ch. Chirality-controlled synthesis of SWNTs remains one of the most challenging topics in SWNT growth research. Understanding of the growth mechanism of SWNTs is critical for the development of a chirality control synthesis technique. Chemical vapor deposition (CVD) is one of the most widely used generation techniques of SWNTs. In CVD methods, SWNTs grow from nano-particles, which are called the catalyst. SWNTs form via the high-temperature reaction between the catalyst particles and carbon-containing gas molecules. Methane or acetylene is generally used as the carbon source. The hydrocarbon molecules are decomposed thermally in the gas phase or decomposed on the catalyst, and carbon atoms are supplied to the catalyst particles. The carbon atoms are re-crystallized by the catalyst and SWNTs are synthesized. When alcohol, such as ethanol or methanol, was used as the carbon source, high-quality SWNTs were generated [2]. When Fe/Co metal particles, which were supported on zeolite particles, were used as catalyst, high-quality SWNTs were Proceedings of the 14th International Heat Transfer Confer nce IHTC14 August 8-13, 2010, Washington, DC, USA